Use final score to generate certificate

We currently want to use the overall final score of the course as the generator for the certificate in Catalog.

The idea I have is to create an assignment, add to the module section (requirement being 70 out of 100) and manually grade the assignment according the the student's final score. The problem is we have over 100 students in the course and that's going to be lots and lots of work and especially time consuming; we'll have students waiting more time for than certificate.